CFD Modeling of Reacting Diesel Sprays with Primary Reference Fuel

Computational fluid dynamics (CFD) modeling has many potentials for the design and calibration of modern and future engine concepts, including facilitating the exploration of operation conditions and casting light on the involved physical and chemical phenomena. As more attention is paid to the matching of different fuel types and combustion strategies, the use of detailed chemistry in characterizing auto-ignition, flame stabilization processes and the formation of pollutant emissions is becoming critical, yet computationally intensive. Therefore, there is much interest in using tabulated approaches to account for detailed chemistry with an affordable computational cost. In the present work, the tabulated flamelet progress variable approach (TFPV), based on flamelet assumptions, was investigated and validated by simulating constant-volume Diesel combustion with primary reference fuels - binary mixtures of n-heptane and iso-octane. Simulations were initially carried out to evaluate and compare the performance of two kinetic models in homogeneous reactors and laminar diffusion flames, followed by turbulent reacting spray simulations considering different fuels, ambient temperatures, and oxygen concentrations. The sensitivity study of the turbulent Schmidt number was then conducted, and results in terms of ignition delay and lift-off length were compared with experimental data to determine a more appropriate global constant. Finally, parametric variations of ambient temperature and oxygen concentration were performed for six fuel blends ranging from PRF0 (n-heptane) to PRF100 (iso-octane), confirming the validity of the TFPV model.